Telephone-switchboard system



Feb. 18, 1930. G. v. KING 5 3 TELEPHONE SWITCHBOARD SYSTEM Filed March 20, 1929 &

HII ml lNl/ENTOP G. 1! KING Q ATTORNEY Patented Feb. 18, 1930 UNITED STATES PATENT OFFICE GERALD V, KING, OF ST. .ALBANS,NEW YORK, ASSIGNOR TO BELL TELEPHONE LA BO- RATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK TELEPHONE-SWITCHBOARD SYSTEM Application filed March 20, 1929.

nates in a single cord and plug for outgoing service and is also equipped with a jack for incoming servlce.

An object of the invention is to give the switchboard attendant suitable calling signals and after a connection is established between two lines to give adequate and selective supervisory signals for both the calling and called lines.

A feature of the invention, whereby the above object is attained, resides in a line circuit arrangement, particularly adaptedfor use in small private branch exchange switchboards, in which a first and a second signal device are associated with each line, the first signal device functioning as a line signal when its associated line is a calling line and as acalling supervisory signal after thecalling line is connected to a called line and said second device functioning as a called supervisory signal when its associated line is a called line. I 1

Other features will appear from the fol-.

lowing description when read in connection with the accompanying drawing wh1ch shows,

in a conventional manner, circuits of a PBX telephone switchboard embodying the invention.

It is believed the invention will be-best understood from a description of the operation of a switchboard constructed-in accordance therewith which is shown as having two local subscribers lines L and L and a trunk line T which extends to a distant central a tively low resistance, thereby permitting sufofiice.

Local comectzon 7 It will be first assumedthat a subscriber (not shown) connected to line L calls, by lifting his receiver from the hook in the usual manner, whereupon the line relay LR oper-.

, liancy.

Serial No. 348,391.

contact 3 of relay LR contact 4 of the sleeve relay 5 and lamp LL to ground.

The switchboard attendant upon noting the lighted lamp answers by operating the key K to the right or talking position, thereby extinguishing lamp LL by opening, at contacts 2, its previously traced energizing circuit. The operators set OT is also bridged across the line.

If it is assumed that the calling subscriber desires connection with another local subscriber reached over line L the attendant inserts plug P of the cord associated with the calling line in the jack J associated with the line L and operates the key K of the called line to the left or ringing position, whereupon ringing current from the source 6 is connected to the line L to actuate the bell at the called subscribers station.

WVhen plug P was inserted in jack J 2 a circuit including supervisory lamp SL of line L was closed, which circuit can be traced from battery, lamp SL sleeve contacts of the jack and plug, upper and lowerresistance winding of relay 5 and the lower normal contacts of supervisory relay 7 to ground. Re-

lay 5 operates in this circuit and, at contacts 4, opens at a second point the previously traced circuit for lamp LL and prepares at contacts 9 an auxiliary path for lighting lamp LL when the line relay LR releases.

It will be noted that until the called subscriber answers the lower winding of relay 5,

which is. of a relatively high resistance, is

short-circuited by the ground on the armature of relay 7 and consequently lamp SL lights in the previously traced circuit for the reason that the upper winding of relay 5 is of relaficient current to flow to effect proper bril- Lamp SL continues to burn until the calledsubscriber answers by lifting his receiver from the hook, whereupon the supervisory relay 7 operates inan obvious circuit,

thereby removing the short circuit from" the hlgh resistance winding of relay 5. This causes a considerable lncrease in the resist- 'ance of the circuit of lamp SL and reduces thecurrent How to such a point that the lamp is substantially extinguished, that is, the filament is not heated sutficiently to cause it to glow. Relay 5, however, remains operated by the current flowing through its two windings in series.

Vhen lamp SL= ceases to g'lo w it signals the attendant that the called subscriber has answered.

When the calling subscriber hangs up, before the plug is removed from the jack, line relay LE releases, thereby closing the circuit, for again lighting lamp LL which was prepared when relay 5 operated. It will thus be noted that the lamp LL which first served as a line signal, later serves as a supervisory signal.

lVhen the called subscriber hangs up, supervisory relay 7 releases again, short-circuiting the high resistance winding of relay 5, thereby causing an increasein the sleeve circuit current which causes the lamp SL to light once more, this time as a signal that the called subscriber has hung up.

If, however, the calling or called 'subscribers desire to attract the attention of the switchboard attendant, it is only necessary to move their switchhook down and up a few times in the usual manner, thereby alternately releasing and operating either relay LR or 7 as the case may be, which will cause the associated lamp LL or SL to flash.

' U on noting that both lamps LL and SL are ighted, the attendant removes plug P from the jack, whereupon the circuit restores to normal.

Trunk connectzon It will now be assumed that the local subscriber on line L, wishes to be connected with a distant central office subscriber, reached over the trunk line T. In this case instead of establishing the connection by means of the calling line plug P the attendant reverses the process and inserts the trunk plug TP in jack J of the calling line, thereby extending the calling subscribers line through to the central ofiice over trunk T which causes the line signal thereat to be displayed inthe usual manner and at the same time 'BIIQIgIZGS' the the calling line'to sucha value that the lamp will not receive sufficient current to light.

When the trunk plug was inserted in the jack J the spring contacts of the jack were opened, thereby cutting off th'e'terininal app'aratus of the line and preventing interference'with the connection it the plug P should be accidentally plugged into another line.

When the conversation'i's completed and the calling subscriber hangs up, the trunk supervisory "relay TS releases, thereby restoring the short-circuit around the high resistance winding of relay 10, thus decreasing the resistance of the sleeve circuit and lighting supervisory lamp SL of the calling line. The calling subscriber can attract the attendants attention in the usual manner by flashing the switchhook, which will alternately release and operate relay TS, which results in flashing lamp SL I If it be assumed that a call arrives over the trunk line T for a local subscriber of line L the operation will be as follows. When the central ofiice operator connects with the trunk and rings in the usual manner, the ring-up or line relay TR Operates, thereby completing an obviouscircuit 'for theline lamp TL to battery through the auxiliary signal relay 1. WVhen relay TR operates, it locks up at its inner contacts to ground at contacts of relay 10, thereby maintaining the line Sig-'1 nal or lamp TL lighted after the ringing-impulse has ceased.

The switch board attendant noting the line signal answers by releasing the trunk key TK to the middle or trunk talking position, thereby bridging her telephone set OT across the trunk in an obvious circuit. Release'of TK opens, at contacts 11, the previously traced lockingcircuit for relay TR which deenergizes and exting'uishes the trunk? 7 key from the talk to the upper or normal positionand rings the desired subscriber by operating the key K to the left or ringing position. When the plug is inserted in thejack, supervisory lamp SL of the line-is 'lighted'in thelow resistance sleevecircuit which includes the upper winding of relay 10 only, the lower and high resistance winding being short-oircuited by'the back contact of trunk supervisory relay TS which is not yet operated due to the fact that the called subscriber has not answered.

When the calledsubscriber answers, supervisory relay TS of the trunk operates, there-- by removing the short-circuit from the lower winding of relay 10 which increases the sleeve circuit resistance sufliciently to extinguish the lamp SL which indicates to the attendant that the calling and called stations are-- in communication.

flSho'uld the linewanted be busy, the attendant may disconnect her telephone set from the trunk for the purpose of listening in on the attendantsteleph-one is disconnected,

mazess As soon as the called line becomes idle, the

attendant may plug the trunk into the jack and ring in the usual manner. In practice, the holding bridge will not be removed until the attendant reconnects her telephone with the trunk by operating TK to the middle or trunk talking position, or until the called subscriber answers, at which time the key 'IK may be restored to the upper or normal position.

The sequence of operation from this point on is the same as previously described for the case in which the station on line L was calling.

From the foregoing it will be noted that each local line has two lamp signals, one associated with thejack sleeve and indicated as SL for example, which serves only as a supervisory signal for its associated line L when this line is the called line, but which performs no function if its associated line is the calling line. The other lamp signal, associated with the cord and line circuit apparatus and indicated, for example, as LL in association with line L, serves two functions, one as a line signal when its associated line initiates a call and later as a supervisory signal therefor when the calling line is connected to the called line.

hat is claimed is:

1. In a telephone system, a line, means for extending said line into connection with other lines, means for extending other lines into connection with said line, a signal device individual to said line responsive to the initiation of a call thereover, means responsive to said first means for disabling said signal device as a calling signal and rendering said signal device responsive to supervisory signals from said line, a second signal device individual to said line, and means responsive to said second means for rendering said second signal device responsive to supervisory signals from said line.

2. In a telephone system, a switchboard, a

calling and a called line terminating thereat, means for interconnecting said lines for conversation, first and second signal devices associated with each of said lines, means associated with said calling line tocause display of its first signal device in response to the call, other means for retiring said signal when the calling line is connnected to the called line and for conditioning it to function as a calling supervisory signal thereafter, and a third means, associated with the calling line, for controlling the second signal associated with the called line, as a called supervisory signal, when'sai'd lines are interconnected. 7

3. In a telephone system, a plurality of lines each terminating in both a calling and a called terminal and so arranged that a called terminal vof one line may be engaged by a calling terminal 01 another line for establishing conversational connectionbetween said lines, a signal device individual to each of saidlines responsive to initiation of calls thereover, means responsive to connectionot a calling line to another, line for disabling said device as a calling signal and for conditioning it to thereafter respond to supervisory signals from said calling line and a second signal device individual to each line responsive to supervisory signals from their associated lines when the. Called terminals of said lines are engaged by calling terminals.

a. In a telephone system, a switchboard, a v

calling and a called line terminating thereat in both a plug and a jack, means comprising the plug of the calling line and the jack of the called line for connecting said lines for conversation, a signal device associated with the calling line responsive to a call incoming thereover, relay means in the calling line for retiring said line signal in response to association of said calling line plug with the called line jack and for conditioning it to respond thereafter to supervisory signal impulses incoming over said calling line, a signal device associated with the called line and second relay means in said calling line responsive to supervisory impulses from the called line for controlling said called line signal device.

5. In a telephone system, a first line, a second line, means for extending said first line into connection with the second line, a'relay and a signal device controlled thereby individual to said first line and responsive to the initiation of a call thereover, means responsive to said first means for disabling said device as a calling signal and for conditioning it to function thereafter as a supervisory signal for said first line, a signal device individual to said second line and a second relay individual to said first line responsive to supervisory signal impulses from said second line for controlling the device of said second line.

6. In a telephone system, a line, means for extending said line into connection with other lines, means for extending other lines 'ato connection with said line, a signal device individual to said line responsive to the initiation of a call thereover, means responsive to said first means for disabling said sig naling device as a calling signal and rendering said signal device responsive to supervisory signal impulses from said line, a second I signal device individual to said line, means responsive to said second means for rendering said second signal device responsive to supervisory signals from said line, and

other means responsive to said second means for rendering said first mentioned device unresponsive to signals from said line.

7. In a telephone system, a switchboard, a plurality of lines terminating thereat, means for interconnecting'said lines for conversation, first and second signal devices associated With each of said lines, said first signal devices functioning as line signals when their associated lines are calling lines and as calling supervisory signals after the calling lines are connected to called lines and said second signal devices functioning as called supervisory signals when their associated lines are called lines.

In witness whereof, I hereunto subscribe my name this 19th day of March, 1929.

GERALD V. KING. 

